JPH09256839A - Catalyst deterioration discriminating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent error discrimination of deterioration in a three way catalyst by computing a deterioration index value indicating a degree of deterioration of the ternary catalyst during execution of air-fuel ratio feedback control, inspecting validity of the computed deterioration index value, and prohibiting deterioration discrimination of the ternary catalyst invalidity. SOLUTION: In an air flow meter 13 provided with a crank angle sensors 15, 16 and a water temperature sensor 19, O2 sensor 113, 114, whose signals are inputted to a control circuit 100, are arranged on the upstream side and on the downstream side of a catalyst converter 112 individually. On the basis of the output from the upstream side O2 sensor 113, an internal combustion engine air-fuel ratio is feedback controlled to a target air-fuel ratio, and on the basis of the output from the downstream side O2 sensor 114 during this feed back control, a deterioration index value indicating a degree of deterioration in the ternary catalyst is computed. Then, deterioration index value and the deterioration determination value are compared with each other, and determination of the catalyst is carried out. In this process, validity of the index value is inspected, and if invalidity is determined, deterioration determination is prohibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration judging device for judging the degree of deterioration of a catalyst provided in an exhaust passage of an internal combustion engine for purifying exhaust gas.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine for an automobile,
As a measure for exhaust gas purification, unburned components (HC,
A three-way catalyst has been used that simultaneously oxidizes CO and reduces nitrogen oxides (NO _x ). In order to enhance the oxidation / reduction capability of such a three-way catalyst, it is necessary to control the air-fuel ratio (A / F) indicating the combustion state of the internal combustion engine to near the stoichiometric air-fuel ratio (window). Therefore, an O ₂ sensor (oxygen concentration sensor) that detects the residual oxygen concentration in the exhaust gas to detect whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio is provided in the exhaust pipe, and the fuel amount is determined based on the output. The air-fuel ratio feedback control that corrects is used.

In the air-fuel ratio feedback control, O
It is necessary to install the _two sensors near the combustion chamber, that is, in the exhaust pipe upstream of the three-way catalyst, but it is unavoidable that the O ₂ sensor output varies. In order to compensate for this variation in the upstream O ₂ sensor output,
Double O ₂ with O ₂ sensor installed downstream of the three-way catalyst
A sensor system has also been realized.

That is, since the exhaust gas is sufficiently agitated downstream of the three-way catalyst and the oxygen concentration of the exhaust gas is almost in equilibrium as a result of passing through the three-way catalyst, the output of the downstream O ₂ sensor is upstream. It changes more slowly than the side O ₂ sensor output and represents the air-fuel ratio of the entire air-fuel mixture. Therefore, the double O ₂ sensor system introduces the sub air-fuel ratio feedback control based on the downstream O ₂ sensor output in addition to the main air-fuel ratio feedback control based on the upstream O ₂ sensor output, and uses it in the main air-fuel ratio feedback control. By correcting the fuel ratio correction coefficient based on the output of the downstream O ₂ sensor, variations in the output of the upstream O ₂ sensor are compensated, and the accuracy of air-fuel ratio control is improved.

However, when the three-way catalyst is deteriorated by the heat of the exhaust gas or lead, it is difficult to sufficiently purify the exhaust gas. Therefore, various devices have been conventionally proposed to detect the degree of deterioration of the three-way catalyst. Has been done. One of them is that the downstream O ₂ sensor detects the degree of decrease in the oxygen storage effect after warming up the three-way catalyst (function to retain excess oxygen and use it for purification of unburned exhaust gas). There is one that detects the degree of deterioration of the catalyst.

For example, Japanese Patent Laid-Open No. 5-98948 discloses that
Upstream and downstream O ₂ during air-fuel ratio feedback control
There is disclosed a catalyst deterioration determination device that obtains a locus length of an output of a sensor and detects a degree of deterioration of a three-way catalyst based on a ratio of these locus lengths.

[0007]

However, in the device according to the above-mentioned proposal, if the vehicle is used under unique conditions, it may be judged that the three-way catalyst is deteriorated although it is not deteriorated. There is. For example, when traveling on a pool of water or snow, only the three-way catalyst may be cooled even after the internal combustion engine is completely warmed up.

That is, since the oxygen storage effect of the three-way catalyst decreases not only due to the deterioration of the three-way catalyst but also due to the temperature drop of the three-way catalyst, when the three-way catalyst is cooled, the three-way catalyst deteriorates. It may be misjudged as a thing. Also because of the very strong state catalytic activity at the time of start of use of the new three-way catalyst, when the temperature of the relatively exhaust gas is high, the three by a reduction reaction of the water gas as _{H 2 O + CO → H 2} + CO 2 Hydrogen gas may be generated in the original catalyst. Although the exhaust gas temperature immediately after the start of use of the three-way catalyst of occurrence brand new hydrogen gas is limited to periods of high output characteristics of the downstream O ₂ sensor with hydrogen gas in the exhaust gas reaching the downstream O ₂ sensor Will be affected.

That is, the O ₂ sensor has a structure in which platinum electrodes are arranged on both sides of a solid electrolyte such as zirconium, and one electrode is brought into contact with exhaust gas and the other electrode is brought into contact with the atmosphere. When the temperature exceeds a predetermined temperature, oxygen in the atmosphere ionized at the atmosphere-side electrode moves to the exhaust gas side in the solid electrolyte due to the difference in oxygen concentration between the atmosphere and the exhaust gas. A current flows from the exhaust gas side electrode to the atmosphere side electrode, and a voltage corresponding to the oxygen concentration difference is generated. That is, the O ₂ sensor detects the residual oxygen concentration in the exhaust gas by taking out this voltage as an output signal.

However, when hydrogen gas having a certain concentration or more exists in the exhaust gas, the movement of oxygen from the atmosphere-side electrode to the exhaust gas electrode is blocked by the hydrogen gas, and the output of the O ₂ sensor. Decreases to an oxygen concentration lower than the actual oxygen concentration. That is, the O ₂ sensor outputs a signal on the richer side than it actually is, and the output characteristic of the O ₂ sensor is biased to the lean side as a whole. That is, even if the exhaust gas reaching the downstream O ₂ sensor has the stoichiometric air-fuel ratio, the downstream O ₂ sensor outputs a rich side air-fuel ratio signal.

Therefore, in the double O ₂ sensor system, even if the exhaust gas reaching the downstream O ₂ sensor has the stoichiometric air-fuel ratio, the air-fuel ratio is controlled to the lean side, so that the oxygen adsorption amount of the three-way catalyst is saturated. As a result, oxygen absorption and release due to the oxygen storage effect does not occur. As a result, the air-fuel ratios on the upstream side and the downstream side are repeatedly changed on the lean side of the theoretical air-fuel ratio, which causes a problem that it is determined that the three-way catalyst is deteriorated.

The present invention has been made in view of the above problems, and in a catalyst deterioration judging device for judging deterioration of a three-way catalyst based on the output of the downstream O ₂ sensor, a vehicle is used under special conditions. It is an object of the present invention to provide a catalyst deterioration determination device that can prevent the occurrence of erroneous determination.

[0013]

FIG. 1 is a basic configuration diagram of a catalyst deterioration determination device according to the present invention. That is, the catalyst deterioration determination device according to claim 1 detects a three-way catalyst provided in the exhaust passage of the internal combustion engine and having an oxygen storage effect, and an air-fuel ratio of the internal combustion engine provided in the exhaust passage upstream of the three-way catalyst. An upstream air-fuel ratio sensor, a downstream air-fuel ratio sensor for detecting the air-fuel ratio of the internal combustion engine provided in the exhaust passage on the downstream side of the three-way catalyst, and an internal-combustion engine air-fuel ratio based on at least the output of the upstream air-fuel ratio sensor. And a deterioration index value indicating the degree of deterioration of the three-way catalyst based on the output of the downstream side air-fuel ratio sensor during execution of air-fuel ratio feedback control by the air-fuel ratio feedback control means. The deterioration index value calculating means for determining whether the catalyst is deteriorated by comparing the deterioration index value calculated by the deterioration index value calculating means with the deterioration determination value. If the deterioration index value calculated by the deterioration index value calculation means in the inspection means is not valid, the determination means, the inspection means for inspecting the validity of the deterioration index value calculated by the deterioration index value calculation means, And a prohibition unit that prohibits the deterioration determination by the deterioration determination unit.

In this device, when the deterioration index value of the three-way catalyst calculated based on the outputs of the upstream side and downstream side air-fuel ratio sensors is not appropriate, the deterioration determination of the catalyst is stopped. In the catalyst deterioration determination device according to claim 2, the deterioration index value calculated this time by the deterioration index value calculating means is within a predetermined range determined based on the deterioration index value calculated before the previous time by the deterioration index value calculating means. Sometimes, the deterioration index value calculated this time is considered to be appropriate.

In this device, the validity check of the deterioration index value is performed based on the deterioration index value calculated before the previous time. The catalyst deterioration determination device according to claim 3 is a stop means for stopping the inspection by the inspection means when the deterioration index value calculated by the deterioration index value calculation means before the previous time is within a predetermined range based on the deterioration judgment value. including.

In this device, the determination of validity is stopped when the deterioration index value calculated before the previous time is out of the predetermined range.

[0017]

FIG. 2 is an overall schematic view showing an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention. FIG.
In the above, an air flow meter 13 is provided in the intake passage 12 of the engine body 10. The air flow meter 13 measures the amount of intake air, for example, has a built-in potentiometer and generates an analog signal proportional to the amount of intake air. This analog signal is input to the A / D converter 101 with a built-in multiplexer in the control circuit 100. The distributor 14 includes a crank angle sensor 15 whose axis converts into a crank angle and generates a reference position detecting pulse signal every 720 °, and a reference position detecting pulse signal every 30 ° which is converted into a crank angle. A crank angle sensor 16 for generating is provided. The pulse signals of the crank angle sensors 15 and 16 are supplied to the input / output interface 102 of the control circuit 100, of which the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 12 is provided with a fuel injection valve 17 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder. The water jacket 18 of the cylinder block of the engine body 10 is provided with a water temperature sensor 19 for detecting the temperature of the cooling water. The water temperature sensor 19 generates an analog signal according to the temperature THW of the cooling water. This analog signal is also supplied to the A / D converter 101.

In the exhaust system downstream of the exhaust manifold 111, three harmful components HC, CO and NO _{x in the} exhaust gas are contained.
Converter that accommodates a three-way catalyst that simultaneously purifies gas
12 are provided. In the exhaust manifold 111,
That is, the upstream side of the catalytic converter 112 is connected to the upstream side O ₂
A sensor 113 is provided, and a downstream O ₂ sensor 115 is provided in the exhaust pipe 114 on the downstream side of the catalytic converter 112. The O ₂ sensors 113 and 115 generate electric signals according to the concentration of oxygen components in the exhaust gas. That is, O
_{The 2} sensors 113 and 115 supply different output voltages to the A / D converter 101 of the control circuit 10 depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.

The control circuit 100 is configured as, for example, a microcomputer system, and includes an A / D converter 10
1, input / output interface 102, CPU 103, RAM 104, ROM 105, backup RAM
106, a clock generation circuit 107, and the like.
Further, the throttle valve 116 in the intake passage 2 is provided with an idle switch 117 that generates a signal LL indicating whether or not the throttle valve 116 is fully closed. The idle state output signal LL is supplied to the input / output interface 102 of the control circuit 100.

Reference numeral 118 denotes a secondary air introduction intake valve for supplying secondary air to the exhaust pipe 11 during deceleration or idling to reduce HC and CO emissions. An alarm 119 is activated when the three-way catalyst of the catalytic converter 112 is deteriorated.

Furthermore, in the control circuit 100, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 17. That is, in the routine described later, the fuel injection amount T
When AU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 1
09 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 17. On the other hand, down counter 1
08 counts a clock signal (not shown), and when the output terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 stops the energization of the fuel injection valve 7. . That is, the above fuel injection amount TAU
Only the fuel injection valve 17 is energized, and therefore the fuel injection amount T
The amount of fuel corresponding to AU is sent to the combustion chamber of the engine body 10.

The CPU 103 generates an interrupt at A /
This is when the input / output interface 102 receives the pulse signal of the crank angle sensor 16 after the A / D conversion of the D converter 101 is completed. The intake air amount data Q and the cooling water temperature data THW of the air flow sensor 13 are fetched by an A / D conversion routine executed at a predetermined time or at a predetermined crank angle and stored in a predetermined area of the RAM 105. That is, the data Q and TH in the RAM 105
W is updated every predetermined time. Further, the rotation speed data N _e is calculated by interruption of the crank angle sensor 16 every 30 ° CA and is stored in a predetermined area of the RAM 105.

The operation of the control circuit 100 shown in FIG. 2 will be described below. 3 and 4 are flowcharts of an air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms. In step 301, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 113 is satisfied. For example, when the cooling water temperature is equal to or lower than a predetermined value, during engine startup, during startup increase, during warm-up increase, power increase, fuel injection amount increase for catalyst overheat prevention, upstream O ₂ sensor 1
When the output signal of 13 is never inverted, the closed loop condition is not satisfied during the fuel cut and the like, and the closed loop condition is satisfied in other cases. When the closed loop condition is not satisfied, the routine proceeds to step 325, where the air-fuel ratio feedback flag XMFB is set to "0" and this routine is ended. In step 325, the air-fuel ratio correction coefficient F
The AF may be 1.0.

On the other hand, if the closed loop condition is satisfied, the process proceeds to step 302. That is, in step 302, the upstream O ₂
The output VOM of the sensor 113 is A / D converted and taken in, and in step 303, it is determined whether the air-fuel ratio is rich or lean depending on whether the VOM is the upstream side comparison voltage V _R1 or less. The upstream side comparison voltage V _R1 is usually the voltage at the amplitude center of the output of the O ₂ sensor, and in this embodiment V _R1 = 0.45V. If VOM ≦ V _R1 , that is, if the air-fuel ratio is lean in step 303, it is determined in step 304 whether the delay counter CDLY is positive.

If an affirmative decision is made in step 304, that is, if CDLY> 0, then CDLY is set to 0 in step 305, and the operation proceeds to step 306. If a negative determination is made in step 304, that is, if CDLY ≦ 0, the process directly proceeds to step 306. In step 306, the delay counter CDLY is decremented, and steps 307 and 308 are executed.
The delay counter CDLY is guarded by the minimum value TDL. In this case, the delay counter CDLY has the minimum value T
When DL is reached, the air-fuel ratio flag F1 is set to "0" (lean) in step 309. The minimum value TDL
Is a lean delay time for holding the determination that the state is rich even if there is a change from rich to lean in the output of the upstream O ₂ sensor 113, and is defined as a negative value.

On the other hand, if VOM> V _R1 in step 303, that is, if the air-fuel ratio is rich, it is determined in step 310 whether the delay counter CDLY is negative, and CDLY <0.
If so, in step 311, CDLY is set to 0 and the process proceeds to step 312. On the contrary, if CDLY ≧ 0, the process directly proceeds to step 312. In step 312, the delay counter CDLY is incremented, and in steps 313 and 314.
The delay counter CDLY is guarded with the maximum value TDR. In this case, the delay counter CDLY has the maximum value T.
When reaching DR, the air-fuel ratio flag F1 is set to "1" (rich) in step 315. The maximum value TDR
Is a rich delay time for holding the determination that the output is the lean state even if the output of the upstream O ₂ sensor 113 changes from lean to rich, and is defined as a positive value.

Next, at step 316, it is judged if the sign of the air-fuel ratio flag F1 is reversed, that is, if the air-fuel ratio after the delay processing is reversed. If the air-fuel ratio is inverted, it is determined in step 317 whether the air-fuel ratio is F0 is "0", that is, whether the air-fuel ratio is lean to lean or lean to rich. If F1 = "0", that is, inversion from rich to lean, step 318
At, FAF ← FAF + RSR and the air-fuel ratio correction coefficient FAF are increased in a skip manner. On the contrary, if F1 = "1", that is, if lean is reversed to rich, in step 319,
FAF ← FAF-RSL and the air-fuel ratio correction coefficient FAF are reduced in a skip manner.

If it is determined in step 316 that the sign of the air-fuel ratio flag F1 is not inverted, step 320,
Integration processing is performed at 321 and 322. That is, step 3
At 20, it is determined whether or not F1 = "0", and F1 = "0".
If it is (lean), FAF ← FAF in step 321.
On the other hand, if F1 = "1" (rich), FAF ← FAF-KIL is set at step 322. Here, the integration constants KIR and KIL are skip amounts RSR and RS.
It is set to be sufficiently smaller than L, and KIR (KIL)
<< RSR (RSL). Therefore, step 321
Indicates that the fuel injection amount is gradually increased in the lean state (F1 = "0"), and step 322 is in the rich state (F1 = "1").
The fuel injection amount is gradually reduced by.

Next, in step 323, step 31
The air-fuel ratio correction coefficient FAF calculated in 8, 319, 321, and 322 is guarded by the minimum value, for example, "0.8" and the maximum value, for example, "1.2". This is to prevent the air-fuel ratio from becoming rich or over lean even if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason.

At step 324, the air-fuel ratio feedback flag XMFB is set to "1" and this routine is ended. Further, the double O ₂ sensor system in this embodiment will be described below as a system in which the skip amount used in the air-fuel ratio feedback control based on the output of the upstream O ₂ sensor is variable.

FIGS. 5 and 6 show the downstream O ₂ sensor 115.
2 is a flowchart of a second air-fuel ratio feedback control routine based on the output VOS of the above, which is executed every predetermined time, for example, 512 ms. In steps 501 to 506, it is determined whether or not the closed loop control condition by the downstream O ₂ sensor 115 is satisfied. For example, the closed-loop condition is not satisfied by the upstream O ₂ sensor 113 (step 50
In addition to 1), the cooling water temperature THW has a predetermined value (for example, 70
(° C) or less (step 502), throttle valve 11
When 6 is fully closed (LL = "1") (step 503),
When the secondary air is introduced, that is, the ASV 118 is open (step 504), a light load, that is, Q / N _e <X.
_When it is ₁ (step 505), the downstream O ₂ sensor 1
When 15 is not activated (step 506), etc., the closed loop condition is not satisfied.

When the closed loop control condition is not satisfied, the routine proceeds to step 519, where the air-fuel ratio feedback flag XSFB is set.
Is reset and this routine ends. When the closed loop control condition is satisfied, the routine proceeds to step 508, the air-fuel ratio feedback flag XSFB is set to "1" and the routine proceeds to step 509. In step 509, the output VOS of the downstream O ₂ sensor 115 is A / D converted and fetched, and in step 510, it is determined whether VOS is equal to or lower than the downstream comparison voltage V _R2 (for example, V _R2 = 0.55V), that is, the air-fuel ratio. Determine whether is rich or lean. The downstream comparison voltage V _R2 is a comparison voltage V _R of the output of the upstream O ₂ sensor 13 in consideration of the fact that the output characteristics are different and the deterioration rate is different due to the influence of exhaust gas upstream and downstream of the catalytic converter 12. It is generally set higher than _R1 , but is not particularly limited.

As a result, if VOS ≦ V _R2 (lean), in step 511, RSR ← RSR + ΔRS (constant value) to increase the rich skip amount RSR, and in steps 512 and 513, RSR is set to the maximum value MAX (for example, 7. 5
%) To guard. On the other hand, in step 514 if VOS> V _R2 (rich), to reduce the rich skip amount RSR as RSR ← RSR-.DELTA.Rs, step 515,
At 516, RSR is guarded by the minimum value MIN (for example, 2.5%). Note that the minimum value MIN is a value at a level at which the transient followability is not deteriorated, and the maximum value MAX is a value at a level at which the drivability does not deteriorate due to the air-fuel ratio fluctuation.

At step 517, the lean skip amount R
SL is calculated by the following formula. RSL ← 10% −RSR In step 518, the skip amounts RSR and RSL are set to RA.
Store in M105 and end this routine. FIG. 7 is a flowchart of the injection amount calculation routine, which is executed at a predetermined crank angle, for example, 360 ° CA. Step 7
In 1, the intake air amount data Q and the rotation speed data N _e are read from the RAM 105 and the basic injection amount TAUP (TAU
P is the injection time for obtaining the stoichiometric air-fuel ratio) is calculated by the following equation.

TAUP ← α · Q / N _e (α is a constant) At step 72, the final injection amount TAU is calculated by the following equation. TAU ← TAUP · FAF · β + γ where β and γ are correction amounts determined by other operating state parameters. In step 73, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection.

When the time corresponding to the injection amount TAU elapses as described above, the flip-flop 109 is reset by the output signal of the down counter 108 and the fuel injection ends. 8 to 11 show a catalyst deterioration determination routine, which is executed every predetermined time, for example, every 4 ms. Then, in steps 801-804, it is determined whether the catalyst deterioration determination execution condition is satisfied.

First, in step 801, the upstream O ₂
The output VOM of the sensor 113 determines whether the air-fuel ratio feedback control is being performed, that is, whether XMFB = "1".
In step 802, the lean monitor determines whether the output VOM of the upstream O ₂ sensor 113 is saturated to the lean side for a predetermined period or longer. In step 803, the rich monitor determines whether the output VOM of the upstream O ₂ sensor 113 is saturated on the rich side for a predetermined period or longer.

In step 804, the downstream O ₂ sensor 1
It is determined whether the air-fuel ratio feedback control based on the output VOS of 13 is being performed, that is, whether XSFB = "1". As a result, during the air-fuel ratio feedback control by the output VOM of the upstream O ₂ sensor 113, that is, XMFB = “1”, the output VOM of the upstream O ₂ sensor 113 is not saturated to the lean side or the rich side, And during the air-fuel ratio feedback control by the output VOS of the downstream O ₂ sensor 15,
That is, only when XSFB = "1", the process proceeds to step 805, and the catalyst deterioration determination is performed.

The steps 802 and 803 are provided because even if the air-fuel ratio feedback control is performed by the output VOM of the upstream O ₂ sensor 113, the upstream O ₂
When the output VOM of the sensor 113 is deviated to either the lean side or the rich side, an integrated value LVO serving as a reference value described later.
This is because M and AVOM cannot be obtained accurately. That is, the catalyst deterioration determination is performed only when the output VOM of the upstream O ₂ sensor 113 fluctuates up and down around the theoretical air-fuel ratio equivalent value.

At step 805, the upstream O ₂ sensor 11
3 to calculate the locus length LVOM _i and the area AVOM _i of the output VOM. Here, LVOM _{i and} AVOM _i are defined by the following equations. LVOM _i = LVOM _i-1 + | VOM _i -VOM _i-1 | AVOM _i = AVOM _i-1 + | VOM _i -V _R1 | where the subscript i is the current routine execution time and i-1 is the previous execution time Is shown (see FIG. 12).

Incidentally, FIG. 12 shows the explanation of the output waveform processing of the sensor.
It is a clear diagram and the sensor output changes for ease of understanding.
The sampling timing interval is
It shows for a long time. Then in step 806
Downstream O_TwoThe locus length LVOS of the output VOS of the sensor 115
_iAnd area AVOS_iLVOS to calculate and by the following formula_i= LVOS_i-1+ | VOS_i-VOS_i-1| AVOS_i= AVOS_i-1+ | VOS_i-V_R2| In step 807, VOM is prepared for the next execution._i-1, L
VOM_i-1, AVOM _i-1, VOS_i-1, LVO
S_i-1, AVOS_i-1To update.

At step 808, the counter CTIME is set.
Count up, and in step 809, the value of CTIME
Exceeds a predetermined value Co. This is the track length LV
OM _i, LVOS_i, Area AVOM_i, AVOS_iIs calculated
It is a measure to measure the monitor time for issuing,
Co is the execution time of this routine corresponding to, for example, about 20 seconds.
Is a number.

If an affirmative decision is made in step 809, that is, if CTIME> Co, the routine proceeds to step 810, where the locus length ratio of the downstream O ₂ sensor 115 output VOS and the upstream O ₂ sensor 113 output VOS ANSINT = LVO.
S _i / LVOM _i and area ratio ARATIO = AVOS
Calculate _i / AVOM _i . In step 811,
It is determined whether or not a stored value ANSIINTG of the locus length ratio, which will be described later, is "0". When an affirmative determination is made, the process goes beyond step 812 to directly proceed to step 813. This is because the stored value ANSIINTG of the trajectory length ratio is stored in the backup RAM 106 in order to retain the value even when the internal combustion engine is stopped.
This is because the stored value ANSINTG of the trajectory length ratio is "0" in the first run after the content of 106 is cleared and the validity cannot be determined in step 812.

When a negative determination is made in step 811, that is, when the stored value ANSINTG of the trajectory length ratio is not "0", the process proceeds to step 812, and the trajectory length ratio AN calculated this time is calculated.
It is determined whether or not SINT is equal to or more than a predetermined value η times the stored value ANSIINTG of the trajectory length ratio. This is a measure to prevent an erroneous determination that the three-way catalyst is deteriorated in a special operating state where the three-way catalyst is cooled even though the internal combustion engine is warmed up. Yes,
In the special operation state, the trajectory length ratio ANS calculated this time
This is a treatment based on the fact that INT becomes extremely larger than the trajectory length ratio in the normal state, that is, the stored value ANSIINTG of the trajectory length ratio. The predetermined value η is a value for determining whether the trajectory length ratio ANSINT calculated this time is appropriate for the trajectory length ratio in the special operation state, and is determined in consideration of variations in the trajectory length ratio.

When the affirmative determination is made in step 812, that is, when it is determined that the engine is in the special operation state, the determination of deterioration of the three-way catalyst is not executed and the routine is directly ended. Conversely, when a negative determination is made in step 812,
That is, when it is determined that the special operation state is not set, in step 813, the trajectory length ratio ANSIINT and the area ratio ARATI.
The presence or absence of catalyst deterioration is determined based on O.

In the present embodiment, the determination of the presence or absence of catalyst deterioration is made using the map shown in FIG. 13A or 13B stored in the ROM 104 of the control circuit 100. That is, FIG. 13 is a map for determining the deterioration. In FIG. 13A, when the trajectory length ratio ANSIINT is within the predetermined range determined by the straight lines A and B, if the area ratio ARATIO is larger than the predetermined value, the catalyst is If there is no deterioration, and it is smaller than a predetermined value, it is determined that the catalyst has deteriorated. The catalyst deterioration may be determined by using the map shown in FIG. 13B to determine whether the locus length ratio ANSIINT and the area ratio ARATIO fall within the shaded region.

In FIGS. 13 (A) and 13 (B), the shaded areas indicate the areas where it is determined that the catalyst has deteriorated. Note that FIG.
Since the thresholds A and B of the locus length ratio ANSIINT and the area ratio ARATIO shown in (4) are actually determined according to the type of catalyst and the air-fuel ratio sensor used, FIG. 13 shows only a general tendency.

If it is determined in step 813 that the catalyst has deteriorated, the alarm flag ALM is set in step 814, and the alarm 19 is activated in step 815. On the other hand, if it is determined in step 813 that there is no catalyst deterioration, the process proceeds to step 816, and the alarm flag ALM is reset. In step 817, the alarm flag ALM is stored in the backup RAM 106 and the process proceeds to step 818.

In step 818, the average value tANSI of the trajectory length ratio ANSIINT used for determining the deterioration of the catalyst.
NT is calculated by the following formula. tANSINT = (n · tANSINT + ANSIN
T) / (n + 1) Here, n is the number of executions of the catalyst deterioration determination up to the previous time. In step 818, if the deterioration determination of the three-way catalyst is performed n or more times during the trip (starting the internal combustion engine and stopping the internal combustion engine after traveling), the average value of the trajectory length used for the deterioration determination is calculated. Processing for storing in RAM 104.

In step 819, it is determined whether or not the stored value ANSIINTG of the trajectory length ratio is larger than a predetermined value ε. The treatment in step 819 is for the following reason. That is, when the trajectory length ratio ANSIINT is large enough to determine that the three-way catalyst is deteriorated, the battery is cleared (the storage content of the backup RAM is cleared by removing the battery), and the stored value of the trajectory length ratio. The ANSI NTG is cleared to "0" and the locus length ratio ANSI NT after that becomes the stored value ANSI NTG. However, due to the variation of the locus length ratio ANSIINT, the locus length ratio ANSI
This is to prevent NT from exceeding a predetermined value η times the stored value ANSINTP and not being negatively determined in step 812 and not performing deterioration determination, and the predetermined value ε is determined in consideration of the variation in the trajectory length.

When the determination in step 819 is affirmative, that is, when the stored value ANSIINTG of the trajectory length is larger than the predetermined value ε, the catalyst has deteriorated to a certain extent or more before the battery is cleared, that is, the deterioration degree is the predetermined value. If it is ε or more, step 820 is skipped and the process proceeds to step 821 to stop updating the stored value ANSIINTG of the trajectory length.
This is because when the degree of deterioration is equal to or larger than the predetermined value ε, the deterioration determination is prioritized over the prevention of erroneous diagnosis.

When a negative determination is made in step 819, that is, when the locus length stored value ANSINTG is smaller than the predetermined value ε, the routine proceeds to step 820.
Update NTG with average value tANSINT and step 82
Proceed to 1. Then, in step 821, all the parameters such as CTIME, VOM _i , and VOS _i are cleared in preparation for the next catalyst deterioration determination, and this routine is ended.

In the above double O ₂ sensor system, the first air-fuel ratio feedback control is performed every 4 ms.
Further, the second air-fuel ratio feedback control is performed every 512 ms because the air-fuel ratio feedback control mainly performs the control by the upstream O ₂ sensor having good responsiveness, and the control by the downstream O ₂ sensor having poor response. It is to do so.

In the present embodiment, the degree of deterioration of the three-way catalyst is determined by using the ratio of the locus lengths of the upstream and downstream O ₂ sensor outputs and the ratio of the area surrounded by both sensor outputs. The present invention is also applied to a catalyst deterioration determination device that determines the degree of deterioration based on parameters that reflect the oxygen storage effect of a three-way catalyst, such as the locus length of the output of the downstream O ₂ sensor, the number of inversions, the inversion frequency, and the inversion period. Is possible.

Further, in the above-mentioned double O ₂ sensor system, other double control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as delay time and integration constant, are corrected by the output of the downstream O ₂ sensor. also O ₂ sensor system, also may be applied to the present invention the double O ₂ sensor system for introducing a second air-fuel ratio correction coefficient. In addition, controllability can be improved by simultaneously controlling two of the step amount, the delay time, and the integration constant. Further, it is also possible to fix one of the skip amounts RSR and RSL and to make only the other variable, instead of the delay times TDR and TDR.
One of the DLs may be fixed and only the other may be variable, or a rich integration constant KIR, a lean integration constant K
It is also possible to fix one of the ILs and make the other variable.

Further, in the above embodiment, O ₂ on the upstream side of the catalyst is used.
Although the double O ₂ sensor system which feeds back the air-fuel ratio to the stoichiometric air-fuel ratio based on the sensor output and the downstream O ₂ sensor output has been described, the present application feeds back the air-fuel ratio to the stoichiometric air-fuel ratio by at least the upstream O ₂ sensor output. Can also be applied to In addition, instead of an air flow meter, a Karman vortex sensor,
A heat wire sensor or the like can also be used.

Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed. However, the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed are calculated. The fuel injection amount may be calculated according to Further, in the above-described embodiment, the internal combustion engine in which the fuel injection valve controls the fuel injection amount to the intake system is described. However, the present invention can be applied to a carburetor-type internal combustion engine.
For example, an air-fuel ratio is controlled by adjusting an intake air amount of an engine by an electric air control valve (EACV), an air bleed amount of a carburetor is adjusted by an electric bleed air control valve, and a main system passage and The present invention can be applied to a device that controls an air-fuel ratio by introducing air into a slow system passage, a device that adjusts an amount of secondary air sent to an exhaust system of an engine, and the like.

Further, although the O ₂ sensor is used as the air-fuel ratio sensor in the above-mentioned embodiment, a CO sensor, a lean mixture sensor or the like may be used. In particular, when a TiO ₂ sensor is used as the upstream air-fuel ratio sensor, control responsiveness is improved, and overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented.

[0060]

According to the present invention, in the catalyst deterioration judging device for judging the deterioration of the catalyst based on the outputs of the upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor, it is possible to detect the deterioration of the catalyst under special conditions. Also, there is less risk of accidentally determining that the catalyst has deteriorated.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a catalyst deterioration determination device according to the present invention.

FIG. 2 is an overall schematic view of an example.

FIG. 3 is a flowchart (1/2) of an air-fuel ratio feedback control routine.

FIG. 4 is a flowchart (2/2) of an air-fuel ratio feedback control routine.

FIG. 5 is a flowchart (1/2) of a second air-fuel ratio feedback control routine.

FIG. 6 is a flowchart (2/2) of a second air-fuel ratio feedback control routine.

FIG. 7 is a flowchart of an injection amount calculation routine.

FIG. 8 is a flowchart of a catalyst deterioration determination routine (1 /
4).

FIG. 9 is a flowchart of a catalyst deterioration determination routine (2 /
4).

FIG. 10 is a flowchart of a catalyst deterioration determination routine (3
/ 4).

FIG. 11 is a flowchart of a catalyst deterioration determination routine (4
/ 4).

FIG. 12 is an explanatory diagram of output waveform processing of a sensor.

FIG. 13 is a graph for determining deterioration.

[Explanation of symbols]

 10 ... Internal combustion engine 17 ... Fuel injection valve 100 ... Control device 112 ... Catalytic converter 113 ... Upstream air-fuel ratio sensor 115 ... Downstream air-fuel ratio sensor

Claims (3)

[Claims] 1. A three-way catalyst provided in an exhaust passage of an internal combustion engine and having an oxygen storage effect; and an upstream air-fuel ratio provided in an exhaust passage upstream of the three-way catalyst for detecting an air-fuel ratio of the internal combustion engine. A sensor, a downstream side air-fuel ratio sensor provided in the exhaust passage on the downstream side of the three-way catalyst for detecting the air-fuel ratio of the internal combustion engine, and a target of the internal combustion engine air-fuel ratio based on at least the output of the upstream side air-fuel ratio sensor An air-fuel ratio feedback control means for controlling the air-fuel ratio, and a deterioration index value indicating the degree of deterioration of the three-way catalyst based on the output of the downstream side air-fuel ratio sensor during execution of air-fuel ratio feedback control by the air-fuel ratio feedback control means. It is determined whether the catalyst is deteriorated by comparing the deterioration index value calculated by the deterioration index value calculating means with the deterioration index value calculated by the deterioration index value calculating means. Deterioration determining means, inspection means for inspecting the validity of the deterioration index value calculated by the deterioration index value calculating means, and if the deterioration index value calculated by the deterioration index value calculating means in the inspection means is invalid If it is, a catalyst deterioration determination device comprising: a prohibition unit that prohibits the deterioration determination by the deterioration determination unit. 2. The inspecting means, wherein the deterioration index value calculated this time by the deterioration index value calculating means is within a predetermined range determined based on the deterioration index value calculated before the previous time by the deterioration index value calculating means. The catalyst deterioration determination device according to claim 1, wherein the deterioration index value calculated this time is regarded as valid at a certain time. 3. The inspection means stops the inspection by the inspection means when the deterioration index value calculated before the previous time by the deterioration index value calculation means is within a predetermined range based on the deterioration determination value. The catalyst deterioration determination device according to claim 2, further comprising stop means.